Photoelectric cell



Aug. 1, 1950 E. A. RICHARDS ErAL PHOTOELECTRIC CELL Filed Jan. 5, 1946INVENTO RS EDWARD A RICHARD-5' WILL/AM E. PEASE Patented Aug 1, 19502,516,916 PHOTOELECTRIC CELL Edward Arthur Richards and Pcase, London,England, assignors, assignments, to Inte of Delaware Application January8 Claims. t

The present invention relates to improvements in the construction ofphotoelectric cells.

Photoelectric cells of the self-generating type are commonly constructedby coating one side of a metal disc or plate with a light-sensitivematerial such as selenium, which is subjected to suitable heat treatmentto convert it to the correct crystalline form. The active surface isthen covered by a layer of conducting material such as gold which is sothin as to be translucent. This is usually accomplished by electrostaticdeposition or by sputtering in a high vacuum. When the finished cell isput into use, it is necessary to make electrical connections to theplate supporting the selenium and to the conducting layer on the surfaceof the selenium. In order to make this latter connection, it is usual tomask the surface and then to apply a ring of alloy with a low meltingpoint to the gold or other metal near the periphery of the disc.Connection is then made by light spring contacts which press on thisring of alloy and on the back of the plate. There are certaindisadvantages in this arrangement, since the contact pressure must beVery light in order to avoid damage to the electronic layer between thegold and the selenium. It is therefore difiicult to make good electricalcontact of a permanent nature and the contacts are liable to corrosionit a trace of moisture is present. The cell isirequently sealed againstthe ingress of moisture by the use of transparent varnish or othermaterial, but this is liable to percolate between the alloy ring and thecontact springs and to produce a had contact.

Similar dimculties have been experienced with dry contact metalrectifiers and as described in our U. 6. Patent No. 2,314,104 filed Feb.23, 1940 and issued March 16, 1943 they have been overcome by insulatingthe semi-conducting layer of selenium or the like from the counterelectrode over a limited area. it is then possible to apply sufiicientcontact pressure to the counter electrode over this limited area toprevent bad contacts without affecting the properties of thesemiconducting layer.

The principal object of this invention is to overcome theabove-mentioned disadvantages by similar methods and to produce a robustassembly which can be rendered moisture-proof in any suitable mannerwithout in any way interfering with the electrical connections to thecell.

This object is achieved according to the invention by providing aphotoelectric cell comprising a metal base plate having a coating oflightnational Standard Electric Corporation, New York,

5, 194s, Serial No. In Great Britain February 6,

William Edward by .mcsne N. Y., a. corporation sensitive material on thesurface thereof, and a 55 2 light-permeable electrically conductingcounterelectrode covering the surface of the light-sensitive material,in which the light-sensitive material is electrically insulated from thecounterelectrode over a limited portion 01" the area covered thereby.

The invention also provides a photoelectric cell comprising a metal baseplate, a coating of light-sensitive material on the surface of the baseplate, thin electrically insulating means covering a limited area of thesurface of the said lightsensitive material, an electrically conductinglayer of diaphanous material covering the re-= malnder of thelight-sensitive surface, a. second layer of electrically conductingmaterial secured to the surface of the said insulating means andextending also over a small portion of the surface of the diaphanouslayer so as to make electrical contact therewith, and terminal meansinsulated from the base plate and clamped in contact with the saidsecond layer over the whole or part of the said limited area. Accordingto a modification, the second layer of conducting material is omittedand the diaphanous layer itself is made to extend over the insulatingmeans so that the terminal means makes direct contact therewith.

in one form of photoelectric cell according to the invention a metaldisc or plate is coated with selenium and subjected to the usual heattreatment, and the portion of the surface to which electrical connectionis ultimately to be made is covered with a suitable electricallyinsulating enamel or varnish, or with-a ring or washer or" paper orother insulating rnaterial firmly cemented to the selenium surface. Theremainder of the surface is then sputtered with gold or othertranslucent or transparent material and finally a layer or a, lowmelting point alloy is applied over the insulated portion so as tooverlap slightly the protected area. Any reasonable amount of pressurecan then he applied over the insulated area without rislz of damage tothe sensitive surface.

Two methods or" construction employing this arran ement will bedescribed. In the first, the selenium-coated disc or plate has a centralhole, and the insulating layer is applied to a central annular areasurrounding this central hole. After the remaining surface has beensputtered with gold, a ring of alloy is sprayed on to at least part ofthis remaining surface so as to overlap slightly the outer circumferenceof the ring of insulation. Whilst this operation is being carried out,the edges of the hole are masked so as to leave a narrow uncoated ringat the center to I avoid the possibility of "cin er-o a short-circuitbetween the alloy and the supporting plate.

In the second arrangement the insulating ring.

is applied near the periphery of the disc before carrying out thesputtering process. A ring of alloy is then sprayed over the insulatedarea, the working surface of the disc being suitably masked in order tolimit the width of the ring. Electrical connection is made by clamping ametal ring on to the disc over the insulated area.

Even when the electrical connection is made at the center, it may beconvenient to apply an additional insulating ring at the periphery sothat the disc may be mounted in a suitable housing and secured firmlyaround the outside edge without risk of damage to the sensitive surface.

Figs. 1 to 8 of the accompanying drawing illustrate several forms of theinvention. Fig. 1 shows a front view of a photoelectric cell having acenter contact arrangement, and Fig. 2 shows a sectional view at 2-2 ofFig. 1.

Fig. 3 shows a back view of a cell having a circumferential contactarrangement, and Fig. 4 shows a sectional view taken at 4-4 of Fig. 3;Fig. 5 shows an enlargement of a detailof Fig. 4; Figure 6 shows anenlarged view of a portion of Figure 2; and Figures 7 and 8 showalternative forms of the arrangements of Figures 2 and 4, respectively.

Referring to Figs. 1, 2 and 6, the photoelectric cell comprises a metaldisc I of the iron group having a coating 2 of selenium applied in anysuitable way and heat treated in the customary manner to develop thedesired properties of the selenium. The disc I has a central hole 1around which is co-axially fixed an annular insulating disc 4, which maybe a varnish or the like applied in any convenient way, or it may be awasher of paper or other suitable insulator firmly cementedor otherwisesecured to the selenium surface. The remainder of the surface of theselenium is then covered by sputtering with a thin translucent layer 5of gold or the like, and an annulus 6 of silver or other suitable lowmelting point alloy is sprayed through a mask over the insulating disc4. The mask should preferably be so designed that the annulus 8 extendsslightly over the surface of the layer 5 so as to make contacttherewith, and so as to allow a narrow uncovered margin round theperiphery of the central hole to prevent short circuiting with the disc.

A bolt 1 with a broad head 8 is passed through v the central hole and isinsulated from the disc I by means of the insulating sleeve 9 andinsulating washer Ill. Terminal punchings II and I2 are provided formaking external connections to the conducting layer 5 and to the disc Irespectively, and the whole assembly is clamped tightly together bymeans of the nuts I3 and I4.

It will be seen that the pressure is exerted over the area covered bythe annular insulating disc 4, so that the sensitive surface is notinjured by the pressure. A good electrical contact is thus ensured, andthe disc may be finished by a moisture proofing varnish without the riskof impairing the electrical contact.

It is to be noted that a broad headed rivet may be used instead of thebolt 1, in which case the nuts [3 and I4 are not required, and the partsare then secured by spreading out the end of the rivet. B

An alternative form of the photoelectric cellis shown in Figs. 3, 4 and5. In this case the disc! has no central hole, and the annularinsulating disc or washer 4 is a narrow ring near theperipheryofthedisc. 'lheallcyannulustisailoa narrow ring sprayed overthe disc or washer -4 and overlapping the sputtered gold layer Islightly on the inside of the ring as shown in Fig. 5. A metal clampingring it is clamped against the annulus I by means of six or othersuitable number of rivets it (or screw bolts) insulated in the mannershown for the bolt 1 in Fig. 1. Two metal terminal rings l1 and II areclamped by the same rivets in electrical contact respectively with thedisc I and with the ring I. These terminal rings are provided withconnecting tags I! and 20.

It should be pointed out that if the gold that is used for thetransparent or translucent or diaphanous layer 5 contains suflicientalloying material to provide the necessary degree of hardness, the alloyannulus 6 could be omitted and the diaphanous layer could be extendedover the surface of the insulating ring 4, as shown in Figures '7 and 8so that'in that case direct contact is made between the bolt 1 (or theclamping ring i5) and the conducting layer 5.

As in the case of Figs. 1 and 2, the disc shown in Figs. 3, 4 and 5could be moisture proofed without any risk of producing a bad electricalcontact.

Reference is also made to copendin'g application Serial No. 639,470,filed January 5, 1946, and which discloses improvements in the form ofthe insulating disc disclosed herein.

What is claimed is:

I l. A photoelectric cell comprising a metal base plate, a coating oflight-sensitive material on the surface of the base plate, thinelectrically insulating means covering a limited area of the surface ofthe said light-sensitive material, an electrically conducting layer oftransparent material covering the remainder of the light-sensitivesurface, a second layer of electrically conducting material covering thesurface of the said insulating means and extending also over a smallportion of the surface of the transparent layer so as to make electricalcontact therewith, and terminal means insulated from the base plate andclamped in contact with the said second layer over at least part of thesaid limited area. 2. A photoelectric cell comprising a metal base platehaving a central hole, a selenium coating on the surface of the baseplate, an annular layer of insulating varnish around the said hole onthe surface of the selenium, a translucent metal layer covering theremainder of the selenium surface, an annular layer of a low meltingpoint metallic alloy covering the said layer of insulating varnish andextending partially over the said metal layer, and electrical terminalmeans clamped in contact with the alloy layer, the contact pressurebeing exerted upon the base plate substantially only over the areacovered by the insulating varnish.

3. A photoelectric cell according to claim 2 in which the base plate hasa central hole surrounded by the said annular layer oi insulatingvarnish, and in which the electrical terminal means comprises a boltinsulated from the plate and passing through the said hole and having ahead clamped in contact with the alloy layer within the area of thelayer of insulating varnish. 4. A photoelectric cell according to claim2 in which the base plate is in the form of a circular disc, the annularlayer of insulating varnish being substantially around the periphery ofthe disc and in which the electrical terminal means comprises a metalclamping ring clamped in contact with the alloy layer within the area ofthe layer of insulating varnish by means of bolts or rivets insulatedfrom the disc.

5. A photo-electric cell comprising a metal base plate having a centralhole, a selenium coating on the surface of the base plate, an annularwasher of insulating material around said hole and attached to thesurface of the selenium, a translucent metal layer covering theremainder of the selenium surface, an annular layer of a low meltingpoint metallic alloy covering the said washer and extending partiallyover said metal layer, and electrical terminal means clamped in contactwith the alloy layer, the contact pressure being exerted upon the baseplate substantially only over the area covered by the insulating washer.

6. A photoelectric cell according to claim 2 in which the translucentmetal layer is a layer of gold.

7. A photo-electric cell comprising a metal base plate having a centerhole, a selenium coating on the surface of said base plate, and annularwasher of insulating material cemented to said selenium coating, atranslucent metal layer covering the remainder of the selenium surface,an annular layer of a low melting point metallic alloy covering the saidannular washer and extending partially over the said metal layer, andelectrical terminal means clamped in contact with the alloy layer, thecontact pressure being exerted upon the base plate substantially onlyover the area covered by the insulating washer.

8. A photoelectric cell comprising a metal base plate having a centerhole, a selenium coating on the surface of said base plate, and annularwasher of insulating material cemented to said selenium coating, atranslucent metal layer covering the remainder of the selenium surface,an annular layer of a low melting point metallic alloy covering the saidannular washer and extending partially over the said metal layer, andelectrical terminal means clamped in contact with the alloy layeragainst substantially only that portion of the alloy covering saidannular washer.

EDWARD ARTHUR RICHARDS. WILLIAM EDWARD PEASE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,970,135 Grondahl et al Aug. 14,1934 2,015,431 McIlvaine Sept. 24, 1935 2,196,830 Hewlett Apr. 9, 19402,226,716 Geisler Dec. 31, 1940

